From owner-freebsd-hackers@FreeBSD.ORG  Fri Apr 18 16:39:08 2014
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115])
 (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id CF62EDCE
 for <hackers@freebsd.org>; Fri, 18 Apr 2014 16:39:08 +0000 (UTC)
Received: from email2.allantgroup.com (email2.emsphone.com [199.67.51.116])
 (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id 94C8E1431
 for <hackers@freebsd.org>; Fri, 18 Apr 2014 16:39:07 +0000 (UTC)
Received: from dan.emsphone.com (dan.emsphone.com [172.17.17.101])
 by email2.allantgroup.com (8.14.7/8.14.7) with ESMTP id s3IGd0Q1083984
 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO);
 Fri, 18 Apr 2014 11:39:00 -0500 (CDT)
 (envelope-from dan@dan.emsphone.com)
Received: from dan.emsphone.com (smmsp@localhost [127.0.0.1])
 by dan.emsphone.com (8.14.7/8.14.6) with ESMTP id s3IGd0lP082940
 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO);
 Fri, 18 Apr 2014 11:39:00 -0500 (CDT)
 (envelope-from dan@dan.emsphone.com)
Received: (from dan@localhost)
 by dan.emsphone.com (8.14.8/8.14.7/Submit) id s3IGd0CF082939;
 Fri, 18 Apr 2014 11:39:00 -0500 (CDT) (envelope-from dan)
Date: Fri, 18 Apr 2014 11:39:00 -0500
From: Dan Nelson <dnelson@allantgroup.com>
To: Sergey Matveychuk <sem@semmy.ru>
Subject: Re: statfs(2)
Message-ID: <20140418163900.GA54186@dan.emsphone.com>
References: <53514ED2.2060904@semmy.ru>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <53514ED2.2060904@semmy.ru>
X-OS: FreeBSD 9.2-STABLE
User-Agent: Mutt/1.5.23 (2014-03-12)
X-Virus-Scanned: clamav-milter 0.98.1 at email2.allantgroup.com
X-Virus-Status: Clean
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7
 (email2.allantgroup.com [172.17.19.78]); Fri, 18 Apr 2014 11:39:00 -0500 (CDT)
X-Spam-Status: No, score=-3.9 required=5.0 tests=ALL_TRUSTED,BAYES_00,
 RP_MATCHES_RCVD,URIBL_BLOCKED autolearn=ham version=3.3.2
X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on
 email2.allantgroup.com
X-Scanned-By: MIMEDefang 2.73
Cc: hackers@freebsd.org
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
 <freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers/>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
 <mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 18 Apr 2014 16:39:08 -0000

In the last episode (Apr 18), Sergey Matveychuk said:
> Hi.
> 
> Tell me please, why f_bfree is unsigned and f_bavail is signed?
> 
> struct statfs {
>   ...
>   uint64_t f_bfree;             /* free blocks in filesystem */
>   int64_t  f_bavail;            /* free blocks avail to non-superuser */
>   ...

f_bavail may become negative on UFS, due to space reserved to the root user
(minfree in the newfs and tunefs manpages).  When the free space becomes
less than minree, f_bavail isn't clamped at zero, but just goes negative.

-- 
	Dan Nelson
	dnelson@allantgroup.com